> import IO
> import List
> main = do
>     putStrLn $ "================"
>     aSeq <- getImageSeq
>     putStrLn $ show aSeq
>     bss <- doEncode [] 0 []
>     putStrLn $ show bss
>     putStrLn $ "================"
>     aList <- downList 3
>     putStrLn $ show aList
>     putStrLn $ "================"
> type Byte = Int
> type Image = [ Byte ]
> type Picture = ( Image )
> type BitStream = [ Int ]
> getImageSeq :: IO [Image]
> getImageSeq = do
>     return  [ [9], [10], [8] ]
> getOnePic :: Int -> IO (Maybe Picture)
> getOnePic cnt = do
>     s' <- getImageSeq
>     let s = drop cnt s'
>     let pic = if length s > 0
>                 then Just ( head s )
>                 else Nothing
>     return pic
> doEncode :: [BitStream] -> Int -> [Picture] -> IO [BitStream]
> doEncode bss cnt refs = do
>     pic <- getOnePic cnt
>     case pic of
>       Just p  -> do
>             let (recpic, bs) = encode refs p
>             let newbss  = bss ++ [bs]
>             let newrefs = recpic : refs
>             let newm    = cnt + 1
>             --putStrLn $ "<debug> - doEncode " ++ (show newbss) ++ " "
>             --                                 ++ (show newm) ++ " "
>             --                                 ++ (show newrefs)
>             result <- doEncode newbss newm newrefs
>             putStrLn $ "<debug> + doEncode " ++ (show newbss) ++ " "
>                                              ++ (show newm) ++ " "
>                                              ++ (show newrefs)
>             putStrLn $ "<debug> \\ returns : " ++ (show result)
>             return result
>       Nothing -> do return bss
> encode :: [Picture] -> Picture -> (Picture,BitStream)
> encode [] ( img ) = -- if there is not any ref
>     let bs = 1 : img
>         recpic = ( img )
>     in  ( recpic, bs )
> encode refpics pic@(img) = -- if there is some ref
>     let bs = 0 : map ( uncurry (-) ) ( ( zip img . head ) refpics )
>         recpic = ( img )
>     in  ( recpic, bs )
> downList :: Int -> IO [Int]
> downList x = do
>     if x >= 0
>       then do
>         let x' = x - 1
>         putStrLn $ "<dbg> > downList " ++ (show x')
>         result' <- downList x'
>         putStrLn $ "<dbg> < downList " ++ (show x') ++ " returns " ++ (show result')
>         let result = x : result'
>         return result
>       else return []